The regeneration of cationic and anionic ion-exchange resins, currently applied for partial or total water demineralization, for treatments or purifications of waste water or of dilute salt solutions, for purifications, separations and recoveries of chemical products, etc., is usually carried out with diluted acid or basic solutions, as for example: 10% hydrochloric acid, 8 to 10% nitric acid, 1 to 5% sulphuric acid, 5% sodium hydroxide, 3% ammonium hydroxide, which do not arise any problems with regard to the resin degradation. The regenerating agent is used in excess of 120 to 200% as against the theoretically necessary quantity, and is thus diluted that its volume shall be of about twice the volume of the ion-exchange resin; the corresponding circulation speed is of 4 to 8 m/h; the usual contacting time within the resin is of about 30 minutes; the resin may be exploited at a useful capacity of about 60% as against the total one. The thickness of the resin layer is of 1000 to 1500 mm. Under these conditions, the regeneration may be carried out conveniently in the same reactor where the fixing on ion exchangers takes place.
During the last time, the specialist literature mentions the use of more concentrated acids for the regeneration of ion exchangers, as, for example, 15 to 22% nitric acid. A known process regenerates the cationic resin with 22% nitric acid and the anionic resin with 7% ammonia solution. When using 40% nitric acid, rapid degradations of the resins are stated. It is considered that the use of 50% nitric acid may even lead to explosions.
By these known processes diluted or relatively diluted salt solutions are obtained by regeneration, whose concentration is carried out in additional facilities for evaporation in stages, at high operation costs. The electro-dialysis in cells, with selective ion exchange diaphragms, does not offer either a more advantageous processing solution.
The fast development of the chemical industry has led to the discharge of waste waters and diluted solutions with anion and/or cation content, in ever larger volumes, whose discharge in rivers and lakes cannot be practiced any longer. The usual purifying methods by neutralization, inactivation or destruction of the components, are neither agreeable any longer. New advantageous technical processes for waste water purification and recovery of the components are called for, which shall also allow the recycling of the purified water.
Among the known technological valorization processes -- waste water concentration in vacuum evaporation facilities, electrodialysis in cells, with selective ion exchange diaphragm, stripping by steam or air -- it seems that the processes based on the use of ion-exchange resins, in discontinuous facilities with fixed bed or in continuous facilities with moving bed, are capable of becoming the most advantageous, and it is toward them that the present invention is directed.